The Secondary Xylem Anatomy of 6 Desert Plants of Caragana

The structures of secondary xylem of 6 species of Caragana, which grow in desert regions of Northwest of China, are described in details. The main quantitative characters are compared with species. And a key to the identification of wood structures of 6 species is given. The main similarities of secondary xylem of these 6 species are as follows: vessels per mm2 very numerous, percentage of multiple vessels high; vessel elements very short, perforations simple and in almost horizontal end walls; intervessel bordered pits alternate and vestured, and vessels with spiral thickenings. Libriform fibres are very short, and usually with thick end walls, and with simple pits. Rays are heigh to very low, and with multiseriate and uniseriate, and with heterogeneous type Ⅰ and Ⅱ. In addition, there are differences in other characters, e.g. vessel distribution, amount of axial parenchyma and distribution, ray frequency, crystals present or absent, and crystal distribution, if present. These differences can be used as the anatomical characters to identify the wood structures of the 6 species. In this article we also discuss the relation between the structure of xylem elements and the environmental influences.     

Foraging strategies of an insectivorous marsupial,Sminthopsis youngsoni (Marsupialia: Dasyuridae), in Australian sandridge desert

This study investigated the effects of predation risk, dune position and microhabitat on foraging of the Lesser Hairy‐footed Dunnart Sminthopsis youngsoni, a small insectivorous marsupial, in the Simpson Desert of western Queensland. The intensity of foraging was assessed by establishing feeding stations (dishes containing mealworms) in open and bush microhabitats at three levels on sand dunes, and recording the numbers of prey taken by dunnarts from the stations after nightly bouts of foraging. Risk of predation was manipulated by provision of artificial illumination at alternate feeding stations on each of five occasions when trials were run. The numbers of mealworms left after feeding bouts varied inconsistently across trials, providing little evidence that dunnarts respond to habitat or predation risk while foraging. These results contrast sharply with studies of arid zone rodents, where foraging is usually sensitive to both predation risk and resource distribution. We suggest that S. youngsoni forages equally in all habitats of its sandridge environment, and experiences relatively low risk of predation whilst doing so.     

腾格里沙漠人工固沙植被中油蒿的生长及生物量分配动态

植物的资源分配模式反映了对环境的生态适应对策。2007年整个生长季, 采用生物量法对腾格里沙漠东南缘固沙植被区半灌木油蒿(Artemisia ordosica)地上部分各器官的生长及资源分配格局动态进行了研究。结果表明: 不同时期各器官的生长速率不同, 光合产物在各器官中的分配也不是等量的, 而是按一定的顺序在不同时期有不同的分配中心; 2007年油蒿的营养生长、繁殖输出、生殖枝大小都显著大于年降水量不足其一半的年份, 而繁殖分配和头状花序大小没有差异; 营养器官生物量大的油蒿总的繁殖输出也大, 但生殖期内营养生长和生殖生长既不同时也不等速, 表明资源分配的权衡(Trade-off)是存在的; 固沙植被建立以后, 随着时间延长, 油蒿的当年总生物量、繁殖输出、繁殖器官生物量分配有减小的趋势, 但不显著。     

Life‐history strategy and extinction risk in the warm desert perennial spring ephemeral Astragalus holmgreniorum (Fabaceae)

This study of Astragalus holmgreniorum examines its adaptations to the warm desert environment and whether these adaptations will enable it to persist. Its spring ephemeral hemicryptophyte life‐history strategy is unusual in warm deserts. We used data from a 22‐year demographic study supplemented with reproductive output, seed bank, and germinant survival studies to examine the population dynamics of this species using discrete‐time stochastic matrix modeling. The model showed that A. holmgreniorum is likely to persist in the warm desert in spite of high dormant‐season mortality. It relies on a stochastically varying environment with high inter‐annual variation in precipitation for persistence, but without a long‐lived seed bank, environmental stochasticity confers no advantage. Episodic high reproductive output and frequent seedling recruitment along with a persistent seed bank are adaptations that facilitate its survival. These adaptations place its life‐history strategy further along the spectrum from “slower” to “faster” relative to other perennial spring ephemerals. The extinction risk for small populations is relatively high even though mean λ _s > 1 because of the high variance in year quality. This risk is also strongly dependent on seed bank starting values, creating a moving window of extinction risk that varies with population size through time. Astragalus holmgreniorum life‐history strategy combines the perennial spring ephemeral life form with features more characteristic of desert annuals. These adaptations permit persistence in the warm desert environment. A promising conclusion is that new populations of this endangered species can likely be established through direct seeding.     

准噶尔荒漠早春短命植物的光合特性及生物量分配特点

准噶尔荒漠分布的早春短命植物不仅具有十分独特的生物学特点,而且在荒漠植物群落演替、物种多样性维持及土壤改良与防治水土流失等方面具有重要的生态学价值。该文运用Li-6400开放式气体交换光合作用测定系统,对分布于准噶尔荒漠的16种早春短命植物生长盛期的净光合速率(P_n)、蒸腾速率(T_r)、水分利用效率(WUE)等特征进行了测定,并对其中7种植物与生长相关的生物量分配特征进行了分析。结果表明:1)16种植物的最大P_n、 最大T_r及WUE分别为8.07~35.96 μmol CO₂·m^-2·s^-1、3.16~29.64 mmol H₂O·m^-2·s^-1、0.54~4.26 μmol CO₂·mmol^-1H₂O;种间最大P_n与最大气孔导度(Stomatal conductance, G_s)之间存在正相关关系,其相关系数为0.77(p<0.05),线性回归斜率为26.36 μmol·mmol^-1;从光合速率对胞间CO₂浓度及光量子通量密度的响应曲线来看,这类植物的表观CO₂补偿点均在4~5 Pa之间(28~30 ℃),表观羧化效率为0.64~1.86 μmol CO₂·m^-2·s^-1·Pa^-1,表观量子效率为0.05~0.06。2)从生物量分配来看,所测植物的个体生物量为0.05~0.39 g;单株总叶面积为 3.24~51.40 cm²;单位叶面积干重为0.40~0.77 g·m^-2,根在总生物量中所占比例为5.72%~19.43%,单株叶面积比在2.92~9.00 m²·kg^-1之间。种间根所占生物量的比与对应的WUE之间的比较分析结果表明,二者之间存在显著的正相关关系,其相关系数r为0.93(p<0.01)。这些结果表明,所观测的早春短命植物具有典型的C₃植物特征,相比其它类型的荒漠植物具有较高的单位叶面积P_n、高T_r及低WUE,并且在生长发育过程中表现出很低的根/地上生物量比、较高的叶面积比和单位叶面积干重,说明它们具有相对高的生长速率,这与其生长发育节律相一致,反映了它们与准噶尔荒漠环境相适应的特点。     

冻融过程对荒漠短命植物种子萌发的影响

荒漠区冻融交替显著改变土壤温度和水分条件,并进一步影响荒漠植物种子萌发.为解析荒漠土壤冻融过程对植物种子萌发的影响,本研究以古尔班通古特沙漠4种典型短命植物[东方旱麦草(Eremopyrum orientale)、卵果鹤虱(Lappula patula)、尖喙拢牛儿苗(Erodiumoxyrrhychum)和条叶庭荠(...     

Water and sodium requirements of field populations of house mice (Mus domesticus) and short-tailed mice (Leggadina lakedownensis) on Thevenard Island, in the arid Pilbara region of Western Australia

The coexistence of the Lakeland Downs short-tailed mouse Leggadina lakedownensis and house mouse Mus domesticus on Thevenard Island, in the arid north of Western Australia, prompted a study to compare their seasonal water and sodium metabolism using tritiated water and sodium-22 as tracers. Fractional water influx rates for M. domesticus (40.3 ± 1.6% total body-water day⁻¹) were significantly higher than those for L. lakedownensis (25.3 ± 1.2% total body-water day⁻¹). Water effluxes were higher in both species of mouse after the passage of a cyclonic storm near the study site. Water flux differences remained significant between species when turnover rates were scaled with body mass. A comparison of water influx rates of M. domesticus with those predicted for field populations of other eutherian rodents showed that rates for M. domesticus on Thevenard Island were higher than expected. In contrast, water influx rates for L. lakedownensis did not differ significantly from expected values for a desert rodent. Rates of sodium influx for M. domesticus (41.7 ± 3.6 mmol kg⁻¹ day⁻¹) were over twice those of L. lakedownensis (19.7 ± 4.8 mmol kg⁻¹ day⁻¹), and were reflected in the significantly higher concentrations of sodium ingested in the diet, and excreted in the urine, of M. domesticus. Furthermore, the rate of water influx was positively correlated with the rate of sodium influx in M. domesticus, suggesting that they were obtaining both water and sodium from the one dietary source. There was no evidence to suggest that mice of either species were experiencing water or sodium stress, because water and sodium influxes and effluxes remained in balance. These results suggest that M. domesticus on Thevenard Island had a higher-than-expected daily water requirement, and may represent a mesic deme of house mice that have yet to adapt to the island environment. Accepted: 9 May 1999     

Habitat Invasibility and Dominance by Alien Annual Plants in the Western Mojave Desert

Patterns of habitat invasibility and alien dominance, respectively measured as species richness and biomass of alien annual plants, were evaluated in association with four habitat factors at the Desert Tortoise Research Natural Area (DTNA) in the western Mojave Desert, USA. Habitat factors varied in levels of disturbance outside (high) and inside (low) the DTNA, and in levels of soil nutrients in washlet (high) and hummock (low) topographic positions, in Larrea-north (high), Larrea-south (medium), and interspace (low) microhabitats near creosote bushes (Larrea tridentata), and during 1995 when rainfall was 207% (high) and 1994 when rainfall was 52% (low) of the long-term average. Dominant alien plants included the annual grasses Bromus rubens, Bromus trinii, and Schismus spp., and the forb Erodium cicutarium. Species richness and dominance of alien annual plants were slightly higher where disturbance was high, and much higher where soil nutrients were high. B. rubens and B. trinii were most dominant in washlets and in the Larrea-north microhabitats during both years. These two species evolved in mesic ecosystems, and appeared to be particularly limited by soil nutrients at this site. Schismus spp. and E. cicutarium were also most dominant in washlets, but their dominance varied between interspaces in 1994 and the Larrea-south microhabitat in 1995. Monitoring to detect the invasion of new annual plants should focus on regions of high rainfall and nitrogen deposition and on washes and beneath-canopy microhabitats. The ecological range of each alien species should be evaluated separately, because their evolutionary origins may greatly affect their patterns of invasion and dominance in the Mojave Desert. This revised version was published online in July 2006 with corrections to the Cover Date.     

小叶锦鸡儿防风固沙林稳定性研究

针对科尔沁沙地小叶锦鸡儿固沙林在持续高温干旱条件下出现稳定性波动的问题。选择2、5、15、35a人工群落和天然群落进行对比研究。探讨了人工小叶锦鸡儿防风固沙林物种多样性在35a间的变化以及对大气持续干旱的抵抗力和对外界干扰的恢复能力。流动沙丘固定后,固沙林内草本植物迅速侵入。其后则缓慢发展并处于相对稳定状态。植物种类数保持在20～23种。但在人工固沙群落中1年生植物在种类数和数量上始终处于优势地位。而天然群落则是多年生植物占优势。人工固沙群落物种多样性指数逐年提高。但明显低于天然群落。在受到大气持续高温干旱的干扰时。人工群落土壤条件极度恶化。出现了明显的干沙层。最深达140cm。叶片含水量极度降低。植物生长停止。沙地植物群落对牲畜取食均具有一定的补偿的能力。在啃食较轻时表现为超补偿现象。通过建立数学模型分析。人工群落个体的补偿点和超补偿点明显低于天然群落。采用冗余理论对植物群落稳定性机制进行了论述。认为冗余结构的变化是导致群落稳定性变化的内在原因。对现有人工小叶锦鸡儿固沙林的稳定性进行了评价。并认为15a左右人工固沙林正处于相对稳定并缓慢发展状态。对于稳定的人工固沙群落应具备以下条件：(1)适于当地环境条件;(2)对外界干扰具有一定的抵抗性和恢复性;(3)具有正常生长发育和自我更新能力;(4)有较为完善的种群结构。